1. Field of the Invention
The present invention relates to a line-type ink-jet recording apparatus which ejects ink from ejection openings to form an image.
2. Description of Related Art
A head of a line-type ink-jet recording apparatus extends in a direction perpendicular to a conveyance direction for a print medium such as a paper. The head includes a unit in a lower face of which many ejection openings that eject ink to a print medium are formed. Pressure chambers communicating with respective ejection openings are formed in an upper face of the unit. In addition, formed within the unit is common ink chambers each corresponding to two or more pressure chambers and storing therein ink which will be supplied to the pressure chambers. Moreover, individual ink passages each extending from an outlet of each of the common ink chambers through a pressure chamber to an ejection opening are formed in the unit. An actuator having layered piezoelectric sheets made of, e.g., a piezoelectric ceramic material is disposed in each region of an upper face of the unit corresponding to each of the pressure chambers. Ink is supplied from an ink tank, and then distributed through the common ink chambers to the respective pressure chambers. Selectively driving the actuators causes corresponding pressure chambers to be reduced in volume, thereby applying pressure to ink contained in the respective pressure chambers. Consequently, the ink is ejected from ejection openings communicating with the pressure chambers.
When many of the actuators are driven at the same timing for the purpose of simultaneous ink ejection from the corresponding ejection openings, the current consumed reaches a high peak value and therefore a power supply having a high capacity is needed. In this case, moreover, there arises a phenomenon that vibration caused upon driving of an arbitrary actuator hinders driving of another neighboring actuator, which is so-called mechanical crosstalk. This deteriorates accuracy in ink ejection. In order to solve these problems, according to a known technique, many ejection openings are classified into multiple groups and the actuators are controlled in such a manner that the ejection opening groups may differ from each other in ink ejection timing (see Japanese Patent Unexamined Publication No. 10-315451).
On the other hand, if the actuators are driven at the same timing, pressure waves which have propagated from pressure chambers communicating with one common ink chamber may resonate to thereby generate a standing wave within the common ink chamber. The standing wave generated within one common ink chamber causes a phenomenon that pressure fluctuation occurs in an arbitrary individual ink passage communicating with the common ink chamber to thereby produce pressure fluctuation in another individual ink passage communicating with the same common ink chamber, which is so-called fluid crosstalk. To what degree the fluid crosstalk via one common ink chamber has influence on ink ejection is related to a timing of ink ejection from the ejection openings and to positions where the individual ink passages are connected to the common ink chamber.
According to the technique disclosed in the aforementioned document, a timing of ink ejection is differentiated among the ejection opening groups. However, each ejection opening ejects ink at the constant timing and therefore fluid crosstalk having a constant magnitude occurs via a common ink chamber. Thus, the problem of fluid crosstalk described above remains unsolved. That is, each ejection opening exhibits a certain lag in ink ejection characteristics, and a resulting printing includes a relatively clear noise, e.g., uneven density, un-uniform diameters and positions of dots, etc.